Heparin and heparan sulfate represent a class of glycosaminoglycans characterized by a linear polysaccharide of D-glucosamine linked to hexuronic acid (Linhardt, R. J. (1991) Chem. Ind. 2, 45-50; Casu, B. (1985) Adv. Carbohydr. Chem. Biochem. 43, 51-134). Heparin and heparan sulfate are complex carbohydrates that play an important functional role in the extracellular matrix of mammals. These polysaccharides modulate and regulate critical biochemical signaling pathways which impinge on normal physiological processes such as cell and tissue morphogenesis, cell-cell interactions, and growth and differentiation. These polysaccharides also play a critical role in various pathologies including wound healing, tumor growth and metastasis, certain neurodegenerative disorders and microbial pathogenesis, to name a few.
Much of the current understanding of heparin and heparan sulfate sequence has relied on studies of their biosynthesis (Linhardt, R. J., Wang, H. M., Loganathan, D., and Bae, J. H. (1992) Biol. Chem. 267, 2380-2387; Lindahl, U., Feingold, D., and Roden, L. (1986) Trends Biochem. Sci. 11, 221-225; Jacobson, I., and Lindahl U. (1980) J. Biol. Chem. 255, 5094-5100; Lindahl, U., and Kjellen, L. (1987) in The Biology of Extracellular Matrix Proteoglycans (Wight, T. N., and Mecham R., eds) pp. 59-104, Academic Press, New York).
Heparan sulfate, which is chemically related to heparin, is present on the cell surface and within the extracellular matrix (ECM) of virtually every mammalian cell type. These heparin-like glycosaminoglycans (HLGAGs) are present in this extracellular environment as protein-polysaccharide conjugates known as proteoglycans. It is increasingly recognized that HLGAGs play much more than a mere structural role as they interact in a functional manner with numerous proteins of the extracellular matrix, such as laminin, fibronectin, integrins, and collagen. As such, HLGAGs (as part of proteolycans) help to define the biological properties of the matrix. These HLGAGs also interact with an array of cytokine-like growth factors and morphogens present within the extracellular matrix by facilitating their biochemical interaction with receptors and by protecting them from proteolytic degradation. For example, heparin potentiates the biological activity of aFGF, as reported by Thornton, et al., Science 222, 623-625 (1983), possibly by potentiating the affinity of aFGF for its cell surface receptors, as reported by Schreiber, et al., Proc. Natl. Acad. Sci. USA 82, 6138-6142 (1.985). Heparin protects aFGF and bFGF from degradation by heat, acid and proteases, as reported by Gospodarowicz and Cheng, J. Cell Physiol. 128, 475-4 84 (1986); Rosengart, et al., Biochem. Biophys. Res. Commun. 152, 432-440 (1988); and Lobb Biochem. 27, 2572-2578 (1988). bFGF is stored in the extracellular matrix and can be mobilized in a biologically active form by the hydrolyzing activity of enzymes such as heparanase as reported by Vlodavsky, et al., Proc. Natl. Acad. Sci. USA 84, 2292-2296 (1987) and Folkman, et al., Am. J. Pathol. 130, 393-400 (1988) and Emerson et. al. Proc. Natl. Acad. Sci. USA 101(14): 4833-8 (2004).
The binding of FGF to heparan sulfate is a prerequisite for the binding of FGF to its high affinity receptor on the cell surface, as reported by Yayon, et al., Cell 64, 841-848 (1991) and Papraeger, et al., Science 252, 1705-1708 (1991). A specific heparan sulfate proteoglycan has been found to mediate the binding of bFGF to the cell surface, as described by Kiefer, et al., Proc. Natl. Acad. Sci. USA 87, 6985-6989 (1990).
Heparin lyases, such as heparinases, are a general class of enzymes that are capable of specifically cleaving the major glycosidic linkages in heparin and heparan sulfate. Three heparinases have been identified in Flavobacterium heparinum, a GAG-utilizing organism that also produces exoglycoronidases, glycosidases, sulfoesterases, and sulfamidases and other enzymes which further act on the lyase-generated oligosaccharide products (Yang, et al. J. Biol. Chem. 260, 1849-1857 (1987); Galliher, et al. Eur. J. Appl. Microbiol. Biotechnol. 15, 252-257 (1982). These lyases are designated as heparinase I (heparinase, EC 4.2.2.7), heparinase II (heparinase II, no EC number) and heparinase III (heparinase EC 4.2.2.8). The three purified heparinases differ in their capacity to cleave heparin and heparan sulfate: Heparinase I primarily cleaves heparin, heparinase III specifically cleaves heparan sulfate; and heparinase II acts on both heparin and heparan sulfate. Several Bacteroides species (Saylers, et al. Appl. Environ. Microbiol. 33, 319-322 (1977); Nakamura, et al. J. Clin. Microbiol. 26, 1070-1071 (1988)) also produce heparin lyases. A heparin lyase has also been purified to apparent homogeneity from an unidentified soil bacterium by Bohmer, et al. J. Biol. Chem. 265, 13609-13617 (1990).